For the wrapping of various pieces, for example coils, wrapping devices known as such are used to perform the wrapping by means of a wrapping film, preferably a thin and transparent stretch film made of plastic. The film roll is normally fitted in film feeding means, which are further placed in a carriage moving along a circular structure and a track formed therein, either around the whole piece or passing through an opening in the central line of the piece.
One wrapping device is disclosed in EP 0 936 142 A2, or corresponding U.S. Pat. No. 6,192,653. If the film is slackened, the film roll can rotate in the opposite direction and the film is rewound on the film roll. Another device is shown in EP 0 936 141 B1, in which the film roll is rotated by means of a motor. One known device is presented in the publication EP 0 544 312 B1, or corresponding U.S. Pat. No. 5,282,347. The device comprises a roll device placed in a carriage and in which the loose film can be accumulated, if necessary.
A problem of prior art is also the change of the film roll, which is a slow operation and requires special structures in the wrapping device.
One example of exchanging the film roll is presented in U.S. Pat. No. 5,755,083, in which the whole film feeding device, i.e. the film carriage, is changed. The problem is, however, the cutting of the circular track and the transfer mechanisms related to it, as well as the slowness of the change. Another alternative to change the film roll is presented in U.S. Pat. No. 4,914,891. The application of this system in a separate film carriage requires a large number of various actuators in the film carriage, increasing its weight and size. Energy supply to a separate, moving film carriage is more difficult than in the device of the reference publication. In view of automatic operation, the correct placement of the film between the guide rolls is a critical step, and its implementation in a reliable manner by using a large variety of guide roll alternatives is difficult.